We have been studying selected immunohistological staining patterns of intraventricular tissue grafts in host brains as well as adrenal medulla in situ and in vitro. We have attempted to determine what factors are essential for completion of the development and survival of these tissues in host brains after transplantation. Results indicate that the expression of cell adhesion molecules (CAMs) in transplanted cerebella is relatively undisturbed. Therefore, it is likely that the molecular mechanisms of granule cell migration are operant in grafts, independently of the normal inputs. Other results indicate that genetically normal cerebellar grafts can survive in a mutant host environment effective in CAMs and myelination. We have found that intraventricular grafts, as compared to intraparenchymal grafts, are not as well integrated with host brains in terms of the presence of interconnecting neurites. Other data further suggest that, only in xenografts, does an intense host reaction occur that is capable of destroying transplanted tissue. Ia immunoreactivity is enhanced in host parenchyma on microglial cells, but not on GFAP positive astrocytes after iso-, allo- and xenografting. Rats receiving xenografts and simultaneously infused antibodies against either Ia antigen or penicillin develop granuloma reactions. Moreover, chronic CSF infusion of antibodies against Ia molecules did not prevent occurrence of immunological reactions and did not enhance the survival of intracerebral xenografts. Other results indicate that CAMs are present in rat adrenal medulla in situ. In tissue culture, the outgrowth of fibers on chromaffin cells is associated with enhancement of Ll/Ng-CAM and N-CAM on their neurites as well as on Schwann cells. Transplanted surviving adrenal medulla fragments within the lateral ventricle of the host rat demonstrated enhancement of Ll/Ng-CAM expression which was accompanied by reorganization of their closely associated extracellular matrix.